SRK2000 STMicroelectronics, SRK2000 Datasheet - Page 13

• Manufacturer Part Number: SRK2000
• Description: SYNCHRONOUS RECTIFIER SMART DRIVER FOR LLC RESONANT CONVERTER
• Manufacturer: STMicroelectronics

SRK2000
5.3
5.4
Figure 8.
Gate driving
The IC is provided with two high-current gate-drive outputs (1 A source and 3.5 A sink),
each capable of driving one or more N-channel Power MOSFETs. Thanks to the
programmable gate-drive UVLO, it is possible to drive both standard MOSFETs and logic
level MOSFETs.
The high-level voltage provided by the driver is clamped at V
excessive voltage levels on the gate in case the device is supplied with a high Vcc.
The two gate drivers have a pull-down capability that ensures the SR MOSFETs cannot be
spuriously turned on even at low Vcc: in fact, the drivers have a 1 V (typ.) UVLO saturation
level at Vcc below the turn-on threshold.
Intelligent automatic sleep-mode
A unique feature of this IC is its intelligent automatic sleep-mode. The logic circuitry is able
to detect a light load condition for the converter and stop gate driving, also reducing the IC’s
quiescent consumption. This improves converter efficiency at light load, where the power
losses on the rectification body diodes (or external diodes in parallel to the MOSFETs) go
lower than the power losses in the MOSFETs and those related to their driving.
The IC is also able to detect an increase of the converter’s load and automatically restart
gate driving.
The algorithm used by the intelligent automatic sleep-mode is based on a dual time
measurement system. The duration of a switching cycle of an SR MOSFET (that is one half
of the resonant converter switching period) is measured using a combination of the
negative-going edge of the drain-to-source voltage falling below V
positive-going edge exceeding V
measured from the moment its body diode starts conducting (drain-to-source voltage falling
below V
the moment the body diode ceases to conduct (drain-to-source voltage going over V
While at full load the SR MOSFET conduction time occupies almost 100% of the switching
cycle, as the load is reduced, the conduction time is reduced and as it falls below 40%
(D
OFF
) of the SR MOSFET switching cycle the device enters sleep-mode. To prevent
TH-ON
Typical connection of the SRK2000 to the SR MOSFET
) to the moment the gate drive is turned off (in case the device is operating) or
I
I
SR1
SR1
SR1
SR1
Doc ID 17811 Rev 2
To Xformer
To Xformer
DVS1,2_A
R
R
R
R
; the duration of the SR MOSFET conduction is
D
D
G
G
DVS1
DVS1
GD1
GD1
SRK2000
SRK2000
GDclamp
DVS1,2_PT
Application information
(=12 V) to avoid
and the
TH-ON
13/17
).